Wind turbine blade molds

ABSTRACT

A mold for a wind turbine blade includes a plurality of spaced-apart joists, each joist having an edge configuration generally corresponding to a form of the blade; and a flexible frame, supported by the edges of the joists, for shaping an exterior surface of the blade.

BACKGROUND OF THE INVENTION

1. Technical Field

The subject matter described here generally relates to fluid reactionsurfaces with vibration damping features, and, more particularly tomolds, and methods of making molds, for use in manufacturing windturbine blades.

2. Related Art

A wind turbine is a machine for converting the kinetic energy in windinto mechanical energy. If that mechanical energy is used directly bymachinery, such as to pump water or to grind wheat, then the windturbine may be referred to as a windmill. Similarly, if the mechanicalenergy is further transformed into electrical energy, then the turbinemay be referred to as a wind generator or wind power plant.

Wind turbines use one or more airfoils in the form of a “blade” togenerate lift and capture momentum from moving air that is them impartedto a rotor. Each blade is typically secured at its “root” end, and then“spans” radially “outboard” to a free, “tip” end. The front, or “leadingedge,” of the blade connects the forward-most points of the blade thatfirst contact the air. The rear, or “trailing edge,” of the blade iswhere airflow that has been separated by the leading edge rejoins afterpassing over the suction and pressure surfaces of the blade. A “chordline” connects the leading and trailing edges of the blade in thedirection of the typical airflow across the blade.

Wind turbines are typically categorized according to the vertical orhorizontal axis about which the blades rotate. One so-calledhorizontal-axis wind generator is schematically illustrated in FIG. 1.This particular configuration for a wind turbine 2 includes a tower 4supporting a drive train 6 with a rotor 8 that is covered by aprotective enclosure referred to as a “nacelle.” The blades 10 arearranged at one end of the rotor 8 outside the nacelle for driving agearbox 12 connected to an electrical generator 14 at the other end ofthe drive train 6 inside the nacelle.

The blades 10 for modern wind generators can be over 80 meters long.Therefore, in order to minimize weight and maximize strength, the blades10 are often formed as fiber-reinforced plastic shells in which a fibermaterial, such as fiberglass, carbon, or aramid is used to reinforce apolymer matrix, such as epoxy, vinylester or polyester thermosettingplastic resin. A hand lay-up technique is most-often used to apply thefabric components against a one-sided mold, after which resin is forcedthrough the individual fiber mats using hand rollers. Once the fabric issaturated with resin, then the excess resin is removed with squeegeesand the part is allowed to cure. Variations on this method includeindividually saturating each fiber mat before it is applied to the moldthrough the use of “pre-preg” material, and/or using applicators thatsaturate each layer before it is added to the mold. However, a widevariety of other techniques are also available for manufacturing suchcomposites, including compression molding, vacuum molding, pultruding,filament winding, resin transfer molding.

The primary advantage of the hand lay-up technique is its suitabilityfor fabricating very large, complex pails with relatively simpleequipment and tooling. that are relatively less expensive than requiredby other manufacturing options. However, such large, complex partsnonetheless require a large and complex mold that can be difficult andcostly to fabricate, especially for prototype components where the costof the mold can not be allocated over a large number of fabricatedcomponents. Even with other, more capital-intensive wind turbine blademanufacturing processes, the cost of preparing the mold is a significantpercentage of the overall cost of manufacturing the blades.

BRIEF DESCRIPTION OF THE INVENTION

These and other aspects of such conventional approaches are addressedhere by providing, in various embodiments, a mold for a wind turbineblade including a plurality of spaced-apart joists, each joist having anedge configuration generally corresponding to a form of the blade; and aflexible frame, supported by the edges of the joists, for shaping anexterior surface of the blade. Also provided is a method of making amold for a wind turbine blade, including the steps of and/or forconfiguring an expanded metal frame to generally correspond to a form ofthe blade; applying a coating to the frame; and machining the coating togenerally correspond with a shape of an exterior surface of the blade.

BRIEF DESCRIPTION OF THE DRAWINGS

Various aspects of this technology invention will now be described withreference to the following figures (“FIGs.”) which are not necessarilydrawn to scale, but use the same reference numerals to designatecorresponding parts throughout each of the several views.

FIG. 1 is a schematic side view of a conventional wind turbine.

FIG. 2 is a partial, schematic orthographic view of a mold for making awind turbine blade.

FIG. 3 is a exploded, partial side view of a method of making a mold fora wind turbine blade using the mold configuration shown in FIG. 2.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 2 schematically illustrates part of a mold for making, all or aportion of, a wind turbine blade 10. Some or all of the blade 10 mayalso be formed using various techniques, such as those described inco-pending, commonly-owned U.S. patent application Ser. Nos. 11/627,490filed on Jan. 26, 2007 as “Preform Spar Cap for a Wind Turbine RotorBlade,” and Ser. No. 11/311,053 filed on Dec. 19, 2005 as “A ModularlyConstructed Rotorblade And Method For Construction.”

The mold 20 includes a plurality of joists 22 arranged on a supportstructure 24. The support structure 24 helps maintain the joists 22 withthe appropriate spacing and height relative to each other. For example,the joists 22 may be 0.1 inch thick metal and/or composite plates thatare spaced apart approximately twenty to thirty inches. However, a widevariety of other materials and/or dimensions may also be used, includingplywood and/or glass reinforced plastic. For example, the joists 22 maybe substantially wider in thickness and/or arranged closely adjacent toeach other. Similarly, although the joists 22 in these illustratedexamples are shown as being supported by a scaffolding-type supportstructure 24, other support structures and/or spacing mechanisms mayalso be used, including simply standing the joists 20 on the ground.

FIG. 3 illustrates is an exploded side view of one of the joists 22 andvertical portions of the support structure 24 in order to describevarious embodiments of a method of malting the mold 20 for a windturbine blade. As with FIG. 2, it must be kept in mind that the varioussteps described here are non-limiting in that they may be combined,including combined with other steps not discussed here, executed withother devices, including other devices not described here, and/orexecuted out of order from the various embodiments shown and discussedhere, including being executed concurrently.

As best illustrated in FIG. 3, the edge 26 of each of the joists 22 hasa configuration generally corresponding to the intended form of theexternal surface of the wind turbine blade 10. In particular, the curvedportion of the edge 26 of the illustrated joists 22 corresponds to achordwise portion of the external surface of the blade 10. However, anyor all of the joists 22 may also be angled relative to the chord of theblade 10, including extending lengthwise in the direction of the span ofthe blade. Similarly, the joists 22 do not have to be arrangedsubstantially perpendicular to the span of the blade 10 and or theground. Consequently, each of the edges 26 of the joists 22 may have aslightly different shape that corresponds to a reverse of the externalsurface topography of the blade 10 at various positions along the blade10. In order to provide precise shapes for the edges 26, each of thejoists 22 may be cut with a numerically controlled saw, or other cutter,in order to achieve a shape as nears as possible to the desired externalsurface of the blade 10.

Once the joists 22 are cut and positioned with appropriate spacing andalignment, a flexible frame 30 is placed over and between each of thejoists 20. For example, the flexible frame 30 may be formed fromexpanded metal plate typically used for decking, including mesh wiretypically used for fencing, and/or plastic sheeting. The stiffness andcorresponding thickness of the plate, wire, sheet, and/or other materialfor the frame 30 is preferably chosen to make it relatively easy toconform to the edges 26 of the joists 22 while still retaining theapproximate curvature of the edges 26 between the joists 22. The use ofadditional joists 22 that are arranged closer together will allow theuse of more flexible material that is easier to conform to the edges 24of the joists 22. Conversely, fewer, further-spaced joist 20 willrequire a stronger, less flexible material for the frame 30 in order tobetter support the mold 20 between the longer spans separating joists22. In either case, the use of a more or less flexible material allowsthe frame 30 to be configured with a shape corresponding to an exteriorsurface of the blade 10 using the edges 26 of the joists 22 as atemplate at each of the joist positions along the span of the blade.

If the flexible frame 30 can be configured with suitable tolerancesrelative to the intended dimensions of the blade 10, then any materialthat is used to form the blade, such as fiber reinforced resin, may beapplied directly to the frame. However, it can be difficult to applysuch materials while maintaining the shape of the frame 30, and toremove the cured blade 10 from the frame. Furthermore, leaving the frame30 in the shell of the blade 10 adds weight and possible surfacedistortions to the blade. Consequently, one or more coatings may bearranged on a side of the frame 30 that is opposite from the joists 22.

In the illustrated embodiment, a first coating layer 32 is arranged onthe frame 30, and an optional second coating layer 34 is arranged overthe low density coating. For example, the first coating 32 may includerigid, semi-rigid, and/or flexible spray foam, such as a polyurethanefoam and/or equivalent polyisocyanurate foam. Such low density,expanding materials for the first coating 32 will fill any openings inthe frame 30, provide improved structural rigidity with little increasein weight, and are relatively easy to machine.

Once the first coating layer 32 is applied and cured, the surface of thelayer 32 may be cut, ground, sanded, and/or otherwise formed to a shapethat more-closely corresponds to the intended external shape of theblade 10. In particular, the layer 32 may be machined withcomputer-controlled equipment so as to provide an exact shape.

Since the first coating layer 32, and/or other materials with similarlysuitable properties, may be relatively fragile, the second coating 34may be applied as a protective layer of higher density material, such asfilled or unfilled plastic resins, including polyester, vinylester,expoxy, and expoxy hybrids such as the DURATEC™ filler coatingsavailable from Durall Plastics. In addition to enhancing durability ofthe mold 20, the optional second coating layer 34 also provides a smoothsurface against which to form the blade 10. However, a variety of othermaterials may also be used for the first and second coating layers 32and 34. The second coating layer 34 may also be polished waxed, and/orbuffed in order to further improved the surface of the blade 10 to beformed with the mold 20.

An optional facesheet 36 may arranged between the first coating layer 32and the second coating layer 34 in order to provide additionalstructural stability to the mold 20. For example, the facesheet 36 maybe formed from composite material, such as a polymeric compositematerial, like fiber-reinforced plastics including glass-reinforcedplastic. Once in place, the facesheet 36 may also be manually formed,directly machined, and/or machined with computer controlled equipment soas to provide an exact shape for the mold 20.

The technology described above provides various advantages overconventional technology. Forming a substantial portion of the mold 20with the flexible frame 30 decreases the cost, weight, and set-up timeassociated with creating the mold. Consequently, the mold 20 isparticularly useful for creating small numbers of prototype parts. Inaddition, the joists 24 are relatively small, lightweight, and easy totransport store as compared a conventional mold. The mold 20 istherefore relatively easy to setup and use a remote construction site inorder to minimize the problems associated with transporting large windturbine blade components.

It should be emphasized that the embodiments described above, andparticularly any “preferred” embodiments, are merely examples of variousimplementations that have been set forth here to provide a clearunderstanding of various aspects of this technology. It will be possibleto alter many of these embodiments without substantially departing fromscope of protection defined solely by the proper construction of thefollowing claims.

1. A mold for a wind turbine blade, comprising: a plurality ofspaced-apart joists, each joist having an edge configuration generallycorresponding to a form of the blade; and a flexible frame, supported bythe edges of the joists, for shaping an exterior surface of the blade.2. The mold recited in claim 1 wherein the flexible frame comprisesexpanded metal.
 3. The mold recited in claim 2, further comprising atleast one coating arranged on a side of the frame that is opposite fromthe joists.
 4. The mold recited in claim 3, wherein the at least onecoating comprises a low density coating arranged on the frame; and ahigh density coating arranged over the low density coating.
 5. The moldrecited in claim 4, wherein the low density coating comprises rigidspray foam.
 6. The mold recited in claim 4, wherein the high densitycoating comprises polyester resin.
 7. The mold recited in claim 6,wherein the high density coating comprises a plastic resin selected fromthe group consisting of polyester, vinylester, epoxy, and hybridsthereof.
 8. The mold recited in claim 7, further comprising a polymericcomposite facesheet arranged between the high density coating and thelow density coating.
 9. The mold recited in claim 1, wherein the joistsare arranged chordwise relative to the blade.
 10. The mold recited inclaim 9 wherein the flexible frame comprises expanded metal.
 11. Amethod of making a mold for a wind turbine blade, comprising the stepsof: configuring an expanded metal frame to generally correspond to aform of the blade; applying a coating to the frame; and machining thecoating to generally correspond with a shape of an exterior surface ofthe blade.
 12. The method recited in claim 11, wherein the coatingcomprises rigid spray foam.
 13. The method of claim 12, furthercomprising the step of applying a protective coating over the machinedrigid foam.
 14. The method recited in claim 13, wherein the protectivecoating comprises a plastic resin selected from the group consisting ofpolyester, vinylester, epoxy, and hybrids thereof.
 15. The methodrecited in claim 14, further comprising the step of arranging apolymeric composite facesheet between the machined foam and thepolymeric resin protective coating.
 16. A method of making a mold for awind turbine blade, comprising: a step for configuring an expanded metalframe to generally correspond to a form of the blade; a step forapplying a coating to the frame; and a step for machining the coating togenerally correspond with a shape of an exterior surface of the blade.17. The method recited in claim 16, wherein the coating comprises rigidspray foam.
 18. The method of claim 17, further comprising a step forapplying a protective coating over the machined foam.
 19. The methodrecited in claim 18, wherein the protective coating comprises a plasticresin selected from the group consisting of polyester, vinylester,epoxy, and hybrids thereof.
 20. The method recited in claim 19, furthercomprising a step for arranging a polymeric composite facesheet betweenthe machined foam and the protective coating.